Particle-in-Cell Modeling of Electron-Beam Generated Low Electron Temperature Plasma

Plasmas generated using electron beams are known to have low electron temperature (T_e) and plasma potential, which are particularly useful for atomic-precision plasma processing. Electron beam produced plasmas are typically confined using a magnetic field and operated at low gas pressures. Previous hybrid modeling of these plasmas indicated that plasma transport can be non-classical in this parameter regime. A self-consistent 2-dimensional particle-in-cell model of electron beam produced plasmas is described. The model examines the creation and evolution of plasma in low pressure (10 – 40 mTorr) Ar on injection of 2 keV electron beam. The plasma is well-confined by the magnetic field with the plasma more constricted around the beam axis at lower pressure and higher magnetic field. Physical and energy transport in the plasma (i.e., ambipolar diffusion and thermal conduction) are observed to scale differently with magnetic field and gas pressure. The charged species density is, for example, found to be more confined near the electron beam axis than T_e. The effect of gas pressure, magnetic field and beam current are examined in the paper. The impact of these parameters on electron density, plasma potential and T_e are found consistent with probe-based experimental measurements.